New:
- new frame for legendaries
- he/she becoming they/them
- a legendary card in each booster
- adding mana is shorter: Add G.
- cost reductions mechanic if you control a wizard (might be other condition)
- weird new enchantment sub type, kind of a revisited cumulative upkeep level up cross
- a mechanic that cares about "historic" things, that are artifacts, legendaries and the new enchantments
- historic or legendary instants/sorceries, you can play them if you control a legendary

note: for whatever reason, goblin in the translation should be elf, as ghost should be goblin : D
also, I've got those from reddit, so no guarantee that all of them are legit

Simone
{green}{white}
Legendary Creature - Human/Warrior
0/0
After the Western Conference, Shanna cannot be the target of an opponent’s ability to control.
Every time you control a creature, Shana gets +1/+1.

Isolated Chapel
Land
Unless you control the plains or swamps, orphaned chapels must be tapped into the battlefield.
{ tap } : Add { white } or { black } .

Jaya Ballard
2RRR (5)
The legendary planewalker ~ Jaya
+1 : Add RRR to your mana pool. This magical power can only be used to cast instant or sorcery spells.
+1 : Discard up to three cards, then draw the same amount of cards.
?8 : You receive the Emblem “You can cast momentary and sorcery cards from your graveyard. If the cards you cast in this way are put into your graveyard, replace them with the emblem”.

Amber
{zero}
Legendary artifact
{Tap}: Adds a little magical power, the color of which is the color of any of the legendary creatures and planeswalkers you control.

Dominaria Heroes Thaifil
{3}{white}{blue}
Legendary Planewalker - Taifei Li
4
+1: Draw a card. At the beginning of the next end step, reset both places.
?3: Place the target nonland permanent at the third position of the top of its owner's library.
?8: You get the badge with the words “Whenever you draw a card, banishes the target’s permanent that is controlled by your opponent.”

Krishna Kahn
{four}
Legendary planewalker ~ Kahn
5
+1: Shows two cards on top of your library. Any opponent chooses one from them. Put the card on your hand and exile another card with a silver counter on it.
?1: Put a card that you own and has silver counters on it from your exile zone.
?2: Sends a 0/0 colorless structure artifact artifact creature and has "If you control an artifact, this creature gets +1/+1."

Bad Knight
{ 1 }{ Black }
Creature - Human/Knight
2/2
First attack
Anti-evil (This creature cannot be the target of white spells or abilities that opponents control.)
As long as any player controls a white permanent, the bad rider gets +1/+0 .

Lich Control
{ 3 } { black }{ black }{ black }
Legendary Enchantment
Evil
Your game will not lose.
Whenever you get life, draw the same amount of cards.
Whenever you lose your life, every time you lose 1 life, choose a permanent that you control or a card in your hand or graveyard and exile.
When the Lich takes control of leaving the battlefield, you lose the game.

Mouse community
{1}{Black}
Creature - Mouse
2/1
For every other mouse you control, your mouse community gets +1/+0 .
The name is the card of the rat community. There is no limit to the number of cards in the deck.

Oath of Teferi - 3WU
Legendary Enchantment
When ~ enters the battlefield, exile another target permanent you control. Return that permanent to the battlefield under it's owner's control at the beginning of the next end step.
You can activate loyalty abilities of planeswalkers you control twice per turn.

Stabilization Orb - 2
Artifact
If a land would produce more than one mana, it produces {C} instead.
Spells cost 1 more to cast for each other spell cast by that spell's owner that turn.

Legionnaire's Helm - 4
Legendary Artifact - Equipment
At the beginning of combat on your turn, create a token that's a copy of equipped creature, except if equipped creature is legendary, the copy isn't. The token gains haste until end of turn.
Equip 5

Solan Blue (???) - 5W
Enchantment - Chronicle
(When ~ enters the battlefield and during your upkeep, put a chronicle counter on ~, then activate the corresponding effect. Sacrifice ~ after the third chronicle counter has been placed.)
1: Destroy all lands.
2, 3: Each player may return up to two target land cards from their graveyard to the battlefield.

Gerrard's Triumph - 1W
Enchantment - Chronicle
(When ~ enters the battlefield and during your upkeep, put a chronicle counter on ~, then activate the corresponding effect. Sacrifice ~ after the third chronicle counter has been placed.)
1, 2: Put a +1/+1 counter on target creature with the greatest power or tied for the greatest power amongst creatures you control.
3: Target creature with the greatest power or tied for the greatest power amongst creatures you control gains flying, first strike, and lifelink until end of turn.

Mirari's Teachings - 4U
Enchantment - Chronicle
(When ~ enters the battlefield and during your upkeep, put a chronicle counter on ~, then activate the corresponding effect. Sacrifice ~ after the third chronicle counter has been placed.)
1: Return target instant card from your graveyard to your hand.
2: Return target sorcery card from your graveyard to your hand.
3: When you cast a instant or sorcery spell this turn, copy it. You may choose new targets for the copy.

Future Vision - 3U
Enchantment
You may look at the top card of your library. (You can do this any time.)
If the top card of your library is an instant or sorcery card, you may cast it.
3: Exile the top card of your library.

Mage's Denial - 1UU
Instant
If you control a Wizard, ~ costs 1 less to cast.
Counter target spell.

???'s Great Rebirth - 5WB
Legendary Sorcery
(You can only cast legendary sorceries if you control a legendary creature or planeswalker.)
Return all legendary permanent cardsfrom your graveyard to the battlefield.

Corrupt Tree Tower (???)* - 3BGU
Legendary Creature
You may cast permanent cards in your graveyard as though they were if your hand, but only one of each type per turn.
6/6

Jaya's Fire Purgatory
XRR
Legendary Sorcery
(Cast a legendary spell only when you control a legendary creature or planeswalker)
~ deals X damage to up to three targets each.

As it is it's a bunch of gobbledygook, not much to talk about with that.

I assume most people are following a similar approach as me and using Google to translate the whole page. When browsing in Chrome, it generally tends to recognize pages in a foreign language and offers to translate the page for you. Granted, all we have is roughly translated information, but that's still a lot of information that shouldn't be out yet.

New:
- new frame for legendaries
- he/she becoming they/them
- a legendary card in each booster
- adding mana is shorter: Add G.
- cost reductions mechanic if you control a wizard (might be other condition)
- weird new enchantment sub type, kind of a revisited cumulative upkeep level up cross
- a mechanic that cares about "historic" things, that are artifacts, legendaries and the new enchantments
- historic or legendary instants/sorceries, you can play them if you control a legendary

note: for whatever reason, goblin in the translation should be elf, as ghost should be goblin : D
also, I've got those from reddit, so no guarantee that all of them are legit

Simone
{green}{white}
Legendary Creature - Human/Warrior
0/0
After the Western Conference, Shanna cannot be the target of an opponent’s ability to control.
Every time you control a creature, Shana gets +1/+1.

Isolated Chapel
Land
Unless you control the plains or swamps, orphaned chapels must be tapped into the battlefield.
{ tap } : Add { white } or { black } .

Jaya Ballard
2RRR (5)
The legendary planewalker ~ Jaya
+1 : Add RRR to your mana pool. This magical power can only be used to cast instant or sorcery spells.
+1 : Discard up to three cards, then draw the same amount of cards.
?8 : You receive the Emblem “You can cast momentary and sorcery cards from your graveyard. If the cards you cast in this way are put into your graveyard, replace them with the emblem”.

Amber
{zero}
Legendary artifact
{Tap}: Adds a little magical power, the color of which is the color of any of the legendary creatures and planeswalkers you control.

Dominaria Heroes Thaifil
{3}{white}{blue}
Legendary Planewalker - Taifei Li
4
+1: Draw a card. At the beginning of the next end step, reset both places.
?3: Place the target nonland permanent at the third position of the top of its owner's library.
?8: You get the badge with the words “Whenever you draw a card, banishes the target’s permanent that is controlled by your opponent.”

Krishna Kahn
{four}
Legendary planewalker ~ Kahn
5
+1: Shows two cards on top of your library. Any opponent chooses one from them. Put the card on your hand and exile another card with a silver counter on it.
?1: Put a card that you own and has silver counters on it from your exile zone.
?2: Sends a 0/0 colorless structure artifact artifact creature and has "If you control an artifact, this creature gets +1/+1."

Bad Knight
{ 1 }{ Black }
Creature - Human/Knight
2/2
First attack
Anti-evil (This creature cannot be the target of white spells or abilities that opponents control.)
As long as any player controls a white permanent, the bad rider gets +1/+0 .

Lich Control
{ 3 } { black }{ black }{ black }
Legendary Enchantment
Evil
Your game will not lose.
Whenever you get life, draw the same amount of cards.
Whenever you lose your life, every time you lose 1 life, choose a permanent that you control or a card in your hand or graveyard and exile.
When the Lich takes control of leaving the battlefield, you lose the game.

Mouse community
{1}{Black}
Creature - Mouse
2/1
For every other mouse you control, your mouse community gets +1/+0 .
The name is the card of the rat community. There is no limit to the number of cards in the deck.

Oath of Teferi - 3WU
Legendary Enchantment
When ~ enters the battlefield, exile another target permanent you control. Return that permanent to the battlefield under it's owner's control at the beginning of the next end step.
You can activate loyalty abilities of planeswalkers you control twice per turn.

Stabilization Orb - 2
Artifact
If a land would produce more than one mana, it produces {C} instead.
Spells cost 1 more to cast for each other spell cast by that spell's owner that turn.

Legionnaire's Helm - 4
Legendary Artifact - Equipment
At the beginning of combat on your turn, create a token that's a copy of equipped creature, except if equipped creature is legendary, the copy isn't. The token gains haste until end of turn.
Equip 5

Solan Blue (???) - 5W
Enchantment - Chronicle
(When ~ enters the battlefield and during your upkeep, put a chronicle counter on ~, then activate the corresponding effect. Sacrifice ~ after the third chronicle counter has been placed.)
1: Destroy all lands.
2, 3: Each player may return up to two target land cards from their graveyard to the battlefield.

Gerrard's Triumph - 1W
Enchantment - Chronicle
(When ~ enters the battlefield and during your upkeep, put a chronicle counter on ~, then activate the corresponding effect. Sacrifice ~ after the third chronicle counter has been placed.)
1, 2: Put a +1/+1 counter on target creature with the greatest power or tied for the greatest power amongst creatures you control.
3: Target creature with the greatest power or tied for the greatest power amongst creatures you control gains flying, first strike, and lifelink until end of turn.

Mirari's Teachings - 4U
Enchantment - Chronicle
(When ~ enters the battlefield and during your upkeep, put a chronicle counter on ~, then activate the corresponding effect. Sacrifice ~ after the third chronicle counter has been placed.)
1: Return target instant card from your graveyard to your hand.
2: Return target sorcery card from your graveyard to your hand.
3: When you cast a instant or sorcery spell this turn, copy it. You may choose new targets for the copy.

Future Vision - 3U
Enchantment
You may look at the top card of your library. (You can do this any time.)
If the top card of your library is an instant or sorcery card, you may cast it.
3: Exile the top card of your library.

Mage's Denial - 1UU
Instant
If you control a Wizard, ~ costs 1 less to cast.
Counter target spell.

???'s Great Rebirth - 5WB
Legendary Sorcery
(You can only cast legendary sorceries if you control a legendary creature or planeswalker.)
Return all legendary permanent cardsfrom your graveyard to the battlefield.

Corrupt Tree Tower (???)* - 3BGU
Legendary Creature
You may cast permanent cards in your graveyard as though they were if your hand, but only one of each type per turn.
6/6

Jaya's Fire Purgatory
XRR
Legendary Sorcery
(Cast a legendary spell only when you control a legendary creature or planeswalker)
~ deals X damage to up to three targets each.

Karn 4
Planeswalker - Karn
+1: Reveal the top two cards of your library. An opponent puts one into your hand. Exile the other with a silver counter on it.
-1: Choose an exiled card you own with a silver counter on it and put it into your hand.
-2: Create a 0/0 colorless artifact construct token with "This creature gets +1/+1 for each artifact you control"
5 loyalty

Jaya Ballard 2RRR
Planeswalker - Jaya
+1: Add RRR. Spend this mana only to cast instant or sorcery spells
+1: Discard up to three cards, then draw that many cards.
-8: You gain an emblem with "You may cast instant and sorcery cards from your graveyard. When a spell cast this way would go to your graveyard, instead exile it"
5 loyalty

Belzenok 4BB
Legendary Creature - Demon
Flying, Trample
When Belzenok enters the battlefield, exile cards from the top of your library until you exile a nonland card. Put that card into your hand and Belzenok deals 1 damage to you. If it has a converted mana cost of 4 or more, repeat this process.
6/6

Oath of Teferi 3UW
Legendary Enchantment
When Oath of Teferi enters the battlefield, exile target permanent you control. Return that card to the battlefield under its owner's control at the beginning of the next end step.
You may activate each Planeswalker's loyalty abilities twice each turn.

Stablization Ball 2
Artifact
If a land would produce two or more mana, it instead produces C instead (possibly no mana, translation unclear)
Each spell costs an additional X to cast, where X is the number of spells that spell's controller has previously cast this turn

Mudu, Corrupt Tower 3UGB
Legendary Creature - Elemental Avatar
You may cast permanent cards from your graveyard on your turn. You may only cast one card of each type this way per turn.
6/6

Darigaaz Reborn 4RGB
Legendary Creature - Dragon
Flying, Trample, Haste
If Darigaaz would die, instead exile it with three egg counters on it.
At the beginning of your upkeep, if Darigaaz is exiled with egg counters on it, remove one. When you remove the last, return it to the battlefield
7/7

I saw this mentioned above but I thought this was cool so here is more detail:

They found a way to make Legendary Instants and Sorceries (I am pretty sure "Witchcraft" is a translation quirk)

New Mechanism: Legendary Witchcraft

The new Legendary Witchcraft card debuted in the Dominaria series, setting the plate for the extraordinary moments of the past. However, these powerful spells can be cast only if there are legendary creatures or planeswalkers to help out.

The death of KSA
{4}{white}
Legendary Witchcraft
(Only you can cast Legendary Witchcraft when you control Legendary Creature or Planeswalker.)
Exile all non-legend non-land permanents.

* Unless you control legendary creatures or legendary planeswalkers, you cannot cast legendary sorcery. Once you begin to cast legendary sorcery, losing the control of the legendary creature and planeswalker at this time will not affect the spell.

* Except for casting restrictions, the legendary Super Category on Witchcraft itself does not add any other rule constraints. You can cast any number of legendary sorcery in a turn, and your deck can contain any number of legendary cards (but no more than four cards of the same name).

Also, more info on the Planeswalker Redirect rule:

Rule Change: Damage cannot be transferred to Planeswalker

Previously, if the source you control will cause non-combat damage to an opponent, you can transfer that damage and instead cause the source to deal damage to one of the planeswalkers controlled by that opponent. This rule will be removed from the game as the Dominaria series goes on sale. A large number of cards that cause a certain amount of damage to the "target player" will receive errata. The principle of errata is:

• The target creature or player marked in the ability is changed to any one of the targets.
• The target player marked in the ability is changed to Target player or Planeswalker. However, if the amount of damage done is calculated based on information from the player or the object being manipulated by the player, the ability will not be modified. This type of power will only harm the player.
• The target opponent marked in the ability is changed to the target opponent or planeswalker (also follow the above exception). Such spells and abilities can target Planeswalker you control.
• The ability to cause damage without having to specify a target has not been undone (except for the ability of a bottled woman).

In addition to the above changes, amendments have been made to other cards that will affect the amount of damage done. In particular, the effect of preventing damage to a target can be prevented, and errata can be obtained by following the above principles.

Master lightning strike
{2}{Red}
moment
If you control a magician, this spell is reduced by {2} to cast.
Master lightning strikes deal 3 damage to any target.